Field of the Invention
The present invention relates to an image pickup apparatus, and more particularly, to an image pickup apparatus having a partial readout function or a skip readout function, and a photographing apparatus including the same.
Description of the Related Art
At a factory manufacturing line, an image pickup apparatus for inputting images has come to be used in place of visual inspection conducted by a human inspector. Such an image pickup apparatus is also referred to as a machine vision camera, and used for inspecting various types of components or products with a computer or a digital input/output device. In recent years, in order to improve inspection accuracy, an image pickup apparatus having ten million or more pixels has come to be used. Similarly, in a consumer digital camera, the number of pixels is increasing more and more in order to improve captured image quality.
With the increasing needs for a greater number of pixels and higher image quality, in recent years, as an image pickup element to be used for a camera, a complementary metal-oxide semiconductor (CMOS) sensor of a rolling shutter type is widely used. In the rolling shutter type, lines of image pickup elements are sequentially exposed. Thus, while exposure time for carrying out exposure by a sensor is set by a user, in control in the camera, the exposure is carried out by a line unit corresponding to the set time.
When a moving image is captured by such an image pickup apparatus and a signal is read out from all pixels of a pixel array, readout time is longer as the number of pixels is larger. Consequently, in the case of moving image capturing, the number of captured images per second is reduced. Further, a data amount for outputting a captured video to the outside becomes greater, and thus a fame rate decreases. For example, in the machine vision camera, total readout time changes with the number of pixels for imaging, and the frame rate changes with the number of pixels output to the outside of the image pickup apparatus.
In an inspection system using the machine vision camera, shortening of inspection time is simultaneously demanded. Accordingly, the number of readout pixels is reduced by reading out a pixel signal from only an interest area among those in which images are captured by the camera, thereby increasing a frame rate. When the frame rate can be increased, the inspection time of the entire system can be shortened.
In the rolling shutter type, charge processing for photoelectric conversion and readout processing of a photoelectrically converted signal are closely linked with each other. For example, when the total readout time is shortened by selection of the interest area, charge time of the sensor may be simultaneously shortened.
In Japanese Patent Application Laid-Open No. 2001-078081, there is disclosed a problem in that exposure time shortens when a part of a pixel in array is designated as an interest area to carry out readout only from the interest area while skipping the remaining unnecessary areas. Accordingly, in Japanese Patent Application Laid-Open No. 2001-078081, optimal exposure is achieved by a diaphragm or a gain applied to an image signal.
In Japanese Patent Application Laid-Open No. 2010-181751, there is disclosed an example of improving, in the case of moving image capturing, a moving image response by skipping readout to shorten overall readout time. In this case, edge enhancement is applied in order to improve visibility for a photographer, and improvement is achieved for exposure.
However, in the above-mentioned related art, a gain is applied to achieve optimal exposure. In the related art, while exposure is secured, there is a problem in that image quality deteriorates due to post-processing after photographing. In the inspection use as described above, various exposure time periods are set, and the interest area is frequently changed. As a result, in the related art, there is a problem in that image quality changes each time setting of the interest area is changed. In the camera for inspection, a high-quality and high-definition captured image is required.